GMod is a Sandbox Modification. Using GMod you can pose ragdolls. This means can position people from HL2/CS/DoD and change their faces. A big comic book creating community has popped up around this feature. Using GMod you can build. Take props from HL2/CS/DoD and weld them together to make walls. Axis a wheel to it to create a working car. Rope some cans to the back. A big contraption creating community has popped up around GMod - creating such things as Rube Goldberg devices, catapults, cannons, bridges etc.. Using GMod you can make your own weapons. That's right, make your own weapons. Using Lua you can create a custom weapon to do just about anything. If you're new you can change simple things like rate of fire, models, sounds. If you're awesome the world is your oyster, mass changing guns, melon cannons, jetpacks. GMod gives you the freedom to do any of these things in single player or online with your friends.

This might seem obvious, but be careful not to smash yourself with whatever you're holding with the physgun.

In this version of Garry's Mod, you can now lift NPCs with the physics gun.

Construction

To prevent your creations from 'spazzing', make the individual objects that it is composed of (say, a couple of blast door models) 'non-colliding' with the No Collide tool.

Vending machines float very well. They are useful for many floating contraptions.

Posing

No-Collide is very useful for making ragdoll poses with someone holding something.

Miscellaneous

To make a disco use the lights tool, and attach lights onto other lights.

To make a rotating disco ball, attach a wheel to the roof, put lights on it, then put a ball of some kind in the middle and wireframe it. Make the wheel invisible and watch it spin.

Rollermines are just props with AI. Try attaching constraints to them for hours of fun.

To get up really high (while most likely killing yourself,) spawn a Blast Door, then stand on it and grab it with your physics gun. Press and hold your use key and tap your back key and it'll pull you up really fast. When you get high enough, right-click to freeze the Blast Door. This is good for air-bases, but be careful as if you get to high you'll hit the skybox and be crushed.